Different types of apparatus have been used in the prior art for treating benign and cancerous tumors. For example, x-rays have been applied to a tumor to treat the tumor. Microwave energy has also been applied to a tumor to treat the tumor. Other forms of energy such as optical energy and laser energy have also been applied to a tumor to treat the tumor. The different types of apparatus used to treat tumors have been generally quite large and cumbersome.
The successful treatment of certain types of tumors is more difficult than the treatment of other types of tumors. For example, the successful treatment of brain tumors and other deep seated tumors, (malignant or benign) within a patient's body is more difficult than for superficial tumors. The objective of the treatment is to reduce in size or completely remove the tumor mass by one or more modalities available at the treatment facility. Common modalities are surgery, chemotherapy and x-ray therapy. A modality used alone or in conjunction with one of the above modalities is "tissue heating" or hyperthermia.
It is particularly well known that hyperthermia combined with x-ray therapy improves the complete response to a malignant tumor by a factor of two (2) compared to x-ray therapy alone. Hyperthermia is also known to have a greater effect on benign tumors compared to radiation therapy. Invasive microwave hyperthermia needles have long been known to be successful in treating brain tumors. With hyperthermia, a controlled thermal dose distribution is required for effective treatment of a deep-seated tumor.
Typical localized hyperthermia temperatures normally used for therapeutic treatment of cancer are in the approximately 42.5.degree. C.-45.degree. C. range. This treatment is generally maintained for approximately thirty (30) minutes to sixty (60) minutes. Normal tissue should be maintained below temperatures of 42.5.degree. C.
Ideally, a focussed radiation beam is concentrated at the tumor with minimal energy delivered to the normal tissue surrounding the tumor. Since the hyperthermia antenna beam width is proportional to the electric field wavelength, a small focal region suggests that the radiating wavelength be as small as possible. However, because of propagation losses in tissue, the depth of penetration of electromagnetic waves decreases with increasing transmittal frequency. For example, a radiating frequency of 915 MHz is used for non-invasive treatment of tumors to a depth of about three centimeters (3 cm) beneath the skin surface.
One of the significant problems in heating a tumor with a non-invasive hyperthermia antenna is the formation of undesired "hot spots" in surrounding tissue. This additional undesired heating often produces pain, burns and blistering in a patient. This sometimes requires termination of the treatment. Similar difficulties of irradiating superficial tissue with non-invasive x-ray applicators are sometimes encountered during deep tumor treatments. Thus, apparatus for, and techniques of, administering hyperthermia directly to a deep tumor site with interstitial x-ray applicators are needed.
An "Interstitial X-ray Needle" is disclosed and claimed in U.S. Pat. No. 5,165,093 issued on Nov. 17, 1992, in the names of Robert B. Miller, John R. Smith and Carl A. Muehlenweq as joint inventors and assigned to The Titan Corporation of San Diego, Calif. The x-ray needle includes a tube open at one end to receive electrons and to concentrate the electrons into a beam. An element is disposed at the other end of the tube to convert the electrons to x-rays and to provide for the passage of the x-rays to a tumor in a patient. The converter closes the tube at the other end of the tube. Thus, a fluid such as water is able to pass through a second tube coaxial with the first tube and cool the converter.
The diameter of the tube holding the fluid may be approximately two (2) millimeters. Because of its small size, the needle is able to be inserted into the patient's body to a position adjacent the tumor. The x-ray needle has the capability of locally inducing hyperthermia as a result of the conductive heat generated by the process of converting the electrons in the beam to x-rays. However, heat conduction limits the diameter of the region of the hyperthermic treatment to about six tenths of a centimeter (0.6 cm). Many tumors have a diameter in the order of two centimeters (2.0 cm) to three centimeters (3 cm). Because of limitations in heat conductivity, an x-ray needle alone cannot generate heat in a sufficiently large volume to treat the tumor.
It is known in the prior art that heating patterns in the order of three centimeters (3 cm) can be achieved by using microwave interstitial needles which are preferably cooled as by air. Without any form of cooling, a microwave interstitial needle can heat no more than a region in a diameter of about six tenths of a centimeter (0.6 cm) of tissue safely. It is also known that an optimal reduction in tumor cell survival is provided by x-ray irradiation during hyperthermal treatments--in other words, by simultaneous x-ray and heat treatment. Invasive x-ray needles currently in use do not allow simultaneous irradiation of tumors with x-rays and microwaves.